1. Field of the Invention
The present invention relates to a method for identifying a fuel type or a fuel mixture in an internal combustion engine.
2. Description of the Related Art
Such internal combustion engines are generally known and operated by supplying an air-fuel mixture to the combustion chamber during the intake stroke. To generate the air-fuel mixture, fuel injectors inject and atomize a predefined fuel quantity into an intake manifold which is connected to the combustion chamber via an intake port. A throttle valve disposed in the intake manifold defines the amount of fresh air that is aspirated in the direction of the combustion chamber. The opening of the throttle valve causes an increase in pressure in the intake manifold, which reduces the evaporation tendency of the injected fuel. Together with fuel, which, for example, is sprayed against the intake manifold wall by the fuel injector, fuel is also deposited on the wall of the intake manifold when the throttle valve is opened, due to the reduced evaporation tendency. When the throttle valve is closed, the pressure in the intake manifold is reduced, the evaporation tendency rises, and fuel deposited on the wall evaporates into the intake manifold, which causes an enrichment of the fuel-air mixture. In both cases the fuel quantity supplied to the combustion chamber, i.e., the actual fuel quantity, differs from the intended fuel quantity, i.e., the setpoint fuel quantity.
For this reason it is generally known to adapt the provided fuel quantity that is injected into the intake manifold in such a way that losses or additional quantities of fuel which, for instance, result from the collection or deposition of fuel on the wall are compensated. If such an adaption is not made or is made incorrectly, there is the risk that the fuel-air mixture in the combustion chamber becomes lean or enriched. Power losses or even combustion misses may then occur under these circumstances. On the other hand, if the lost or additional quantities of fuel are taken into account in a fuel injection and if the injected fuel quantity is adapted, it is possible to ensure a steady operation of the internal combustion engine that produces low emissions.
In addition, internal combustion engines are known which are operated using a fuel mixture that includes multiple fuel types or that can be operated using one of several possible fuel type(s). More specifically, internal combustion engines are known for which a fuel mixture that is composed of a different mixture ratio of gasoline and alcohols is provided, especially ethanol and methanol. These internal combustion engines are known as flex-fuel combustion engines, among other designations, and in particular make it possible to utilize gasoline as fuel in the event that the preferred operation of the internal combustion engine on the basis of alcohols is impossible. Such a situation arises, for instance, when the availability of alcohols is restricted in terms of time or locality. However, the operability on the basis of different fuel mixtures also requires that the composition of the air-fuel mixture and the ignition firing point be adapted to the used fuel mixture (especially to its composition), in particular in cases where the composition of the fuel mixture varies. This requires an identification of the fuel mixture or the fuel type. In the related art, the alcohol content is ascertained with the aid of an alcohol sensor. This has the disadvantage that the ascertainment of the fuel composition entails additional expense because an additional detection means, such as an ethanol sensor, must be installed.